(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of improving the contact profile after contact etch in the fabrication of integrated circuit devices.
(2) Description of the Prior Art
In the fabrication of integrated circuit devices, a multi-dielectric layer-structure is often used as the interlevel dielectric layer. For example, U.S. Pat. No. 5,364,804 to Ho et al teaches a multi-dielectric layer including a tetraethoxysilane (TEOS) layer. FIG. 1 illustrates a partially completed integrated circuit device. Semiconductor device structures, including, for example, gate electrodes 12 and source and drain regions 14 have been formed in and on the semiconductor substrate 10. A typical interlevel dielectric layer formed over the semiconductor device structures includes a first layer of TEOS 18 deposited by plasma enhanced chemical vapor deposition (PECVD).cndot.to a thickness of about 1000 Angstroms, a second layer 20 of borophospho-TEOS (BPTEOS) deposited to a thickness of about 3000 Angstroms, and a third layer 22 of PECVD TEOS deposited to a thickness of about 5000 Angstroms. A contact opening is etched through the interlevel dielectric-layer to the underlying semiconductor devices, such as to source/drain region 14 as illustrated in FIG. 2. Because of the etch rate difference between PE-TEOS and BPTEOS, a reentrant contact profile exists after contact etching. That is, as shown in FIG. 2, the BPTEOS layer etches faster horizontally than do the surrounding PE-TEOS layers resulting in a reentrant shape 28 in the BPTEOS layer rather than the vertical shape of the remainder of the contact.
Typically, before the metal conductor is sputtered into the contact opening, a buffered oxide etch (BOE) of 50:1 is performed to remove the native oxide that forms on the sidewalls of the contact opening. The reentrant profile is even more pronounced after the BOE etch. It is difficult to sputter the metal glue layer, such as titanium nitride/titanium, into the reentrant contact opening. The reentrant profile also affects the stability of contact resistance.
U.S. Pat. No. 5,489,553 to Chen teaches a method of gap filling in the TEOS dielectric layer using a hydrofluoric acid (HF) etch.